A graph turns the numbers in a set of data into a picture, so you can compare them at a glance.
A bar graph suits comparing which is largest, a line graph suits seeing how something changes over time, and a pie chart suits seeing what share of the whole each part takes.
When you read a graph, check the title and the units first, then look for the largest and smallest values, the rises and falls, and each part's share.
The three pictures below show favorite fruits, monthly temperatures and daily reading time as bars, Seoul's average monthly temperature as a line, and a survey of favorite subjects as a pie.
Reading a bar graph
📊 Reading a bar graph
①The length of a bar shows the size of the value, so check the scale and the unit on the vertical axis first
②In favorite fruits, the strawberry bar is the longest at 15 people and grape is the shortest at 5
③Comparing the longest and shortest bars, they differ by 15 − 5 = 10 people
④Switch the data button and the same kind of graph compares other data, such as temperatures or reading time
seegongsik.com
A bar graph comparing the chosen data by bar length
Reading change on a line graph
📈 Seeing change on a line graph
①Where the line goes up to the right the value increased, and where it goes down it decreased
②The steeper the line, the faster the change. In Seoul the temperature climbs sharply from 6 °C in March to 13 °C in April
③The warmest month is August at 27 °C and the coldest is January at −2 °C, a difference of 29 °C
④Monthly averages vary a little from year to year, so the values in the picture are rounded estimates
Line only
seegongsik.com
A line graph joining Seoul's average monthly temperatures
Reading shares on a pie chart
Math 35%
seegongsik.com
A pie chart dividing a survey of favorite subjects into shares
🍰 Seeing shares on a pie chart
①The whole circle is 100%, and the size of each slice is the share that item takes
②Math 35%, science 25%, Korean 20%, English 12% and other 8% add up to 100%
③Math and science together make 60%, more than half of the whole
④Multiply a share by the number of people surveyed to get a number of people: out of 200 students, math is 200 × 0.35 = 70
Summary
Bar Graph
bar length = size of the value
Good for comparing which items are bigger or smaller
Line Graph
the steeper the line, the faster the change
Good for seeing rises and falls over time
Pie Chart
slice size = share of the whole (%)
Good for comparing what share of the whole each item takes
🎯 At a glance
①Bar graph: comparing amounts
②Line graph: seeing change over time
③Pie chart: seeing shares of the whole
④Check the title and the units before reading a graph
⑤The same data can call for a different graph depending on what you want to know
Examples & Unit Review
Example 1
In a pie chart, 35% of the students like math best, and 200 students were surveyed. How many students like math best?
1
Part = whole × share = 200 × 35/100.
2
200 × 0.35 = 70, so 70 students.
▸ 70 students
To turn a percentage on a pie chart into a number of people, multiply the total by the share.
Example 2
On a line graph, Seoul's temperature is 6 °C in March and 26 °C in July. By how many degrees did it rise from March to July?
1
Change = later value − earlier value = 26 − 6.
2
26 − 6 = 20, so it rose by 20 °C.
▸ 20 °C
In the picture the line keeps climbing between March and July, which also tells you the temperature rose the whole time.
Unit Review
In a pie chart of 50 students, 20% like Korean best. How many students like Korean best?